Schweitzer Engineering Laboratories SEL-421-4 - Page 1437

18.31
Date Code 20171006 Instruction Manual SEL-400 Series Relays
Synchrophasors
SEL Fast Message Synchrophasor Protocol
In the SEL Fast Message Synchrophasor Protocol, the master device determines
the message period (the time among successive synchrophasor message time-
stamps) in the enable request. If the relay can support the requested message
period on that serial port, the relay acknowledges the request (if an acknowledge
was requested) and commences synchrophasor data transmission. If the relay
cannot support the requested message period, the relay responds with a response
code indicating bad data (if an acknowledge was requested).
The SPEED setting on any serial port set with PROTO := PMU should be set as
high as possible, to allow for the largest number of possible message period
requests to be successful.
The relay Fast Message synchrophasor format always includes 32 bytes for the
message header and terminal ID, time information, frequency, and status bits.
The selection of synchrophasor data will add to the byte requirements.
Table 18.20 can be used to calculate the number of bytes in a synchrophasor message.
Table 18.21 lists the bps settings available on any relay serial port (setting
SPEED), and the maximum message size that can fit within the port bandwidth.
Blank entries indicate bandwidths of less than 40 bytes.
Referring to Table 18.20 and Table 18.21, it is clear that the lower SPEED set-
tings are very restrictive.
Some observations from Table 18.21 follow.
➤ A serial port set with SPEED := 38400 or 57600 can handle any size
message at any data rate.
➤ A serial port set with SPEED := 19200 can handle a single-
synchrophasor or four-synchrophasor message at any data rate, and
any size message as fast as 10 messages per second.
Table 18.20 Size of an SEL Fast Message Synchrophasor Message
Item
Possible
Number of
Quantities
Bytes per
Quantity
Minimum
Number of
Bytes
Median
Number of
Bytes
Maximum
Number of
Bytes
Fixed 32 32 32
Synchrophasors 1, 4, or 8 8 8 32 64
Total (Minimum, Median, and Maximum) 40 64 96
Table 18.21 Serial Port Bandwidth for Synchrophasors (in Bytes)
Requested Message
Period (ms)
Equivalent Message
Rate (messages per
second)
Port Setting SPEED
300 600 1200 2400 4800 9600 19200 38400 57600
1000 1 41 83 166 333 666 1332 2665 3998
500 2 41 83 166 333 666 1332 1999
250 (60 Hz only) 4 41 83 166 333 666 999
200 5 66 133 266 533 799
100 10 66 133 266 399
50 (60 Hz only) 20 66 133 199